Actively sensing and cancelling vibration in a printed circuit board or other platform

ABSTRACT

An embodiment includes generating a sense signal that represents a first vibration of a platform, and reducing a level of the first vibration by generating, in response to the sense signal, a second vibration in the platform. For example, a sensor generates a sense signal representing a first vibration induced (e.g., a shock-induced vibration) in the platform. And a vibration-cancel circuit reduces or eliminates a level of the first vibration in response to the sense signal. For example, the vibration-cancel circuit reduces a magnitude of a first vibration induced in a platform, or eliminates the first vibration altogether, by generating, in the platform, a second vibration having a magnitude approximately equal to the magnitude of the first vibration and having a phase approximately opposite to the phase of the first vibration. That is, the second vibration cancels the first vibration to reduce the net vibration that the platform experiences.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 16/049,658, filed on Jul. 30, 2018, and titled, “Actively Sensingand Cancelling Vibration in a Printed Circuit Board or Other Platform,”which is incorporated herein by reference in its entirety.

SUMMARY

A subassembly or a subsystem, such as an Inertial Measurement Unit(IMU), that includes one or more component platforms, such as aprinted-circuit board (PCB) or a printed-wiring board, and that isdesigned for use in a mobile environment (e.g., for use in vehicles suchas aircraft), may experience shock-induced vibrations in one or moredimensions (shock-induced vibrations are sometimes called “shockvibrations”). For example, such a vibration-inducing shock can be causedby a bump in the road, air turbulence, maneuvering of a vehicle in whichthe subsystem is disposed, collision of a vehicle in which the subsystemis disposed, or a nearby explosion.

FIG. 1 is a plot 10 of a portion of a frequency spectrum ofshock-induced vibration experienced by a PCB of an IMU (not shown inFIG. 1). Such a shock-induced vibration can have a duration on the orderof a few microseconds to a few seconds, and can have a frequencyspectrum in a range that spans from a few Hertz (Hz) to hundreds ofkilohertz (kHz).

A shock-induced vibration, such as plotted in FIG. 1, can temporarilycontort, or otherwise deform, a PCB or other platform, and cantemporarily contort, or otherwise deform, one or more components mountedto the PCB or other platform.

Unfortunately, such deformation can damage a PCB or other platform andthe components mounted to the PCB or other platform. If a shock-inducedvibration is powerful enough, then the deformation due to one shock maybe sufficient to damage a PCB or other platform or one or morecomponents mounted thereto. Alternatively, the cumulative effects ofmultiple deformations caused by multiple shock-induced vibrations maydamage the PCB or other platform, or one or more components mountedthereto, over time.

Furthermore, a shock-induced vibration can introduce error into ameasurement taken by, and a sense signal output by, a sensor componentsuch as an accelerometer or a gyroscope. For example, an externalvibration may give rise to a Vibration Rectification Error (VRE), whichis an error that manifests as an anomalous shift in an offset of theaccelerometer.

A conventional technique for reducing damage to PCBs, other platforms,and components mounted thereto is to mount the PCB/other platform to avibration-damping, or a vibration-isolation, structure that isconfigured to arrest, either partially or fully, a shock-inducedvibration experienced by the PCB/other platform.

FIG. 2 is a diagram of a PCB assembly 20, which includes a PCB 22, a PCBmount 24, and a vibration-isolation structure 26 disposed between thePCB and the mount. And on the PCB 22 are mounted various circuitcomponents 28, such as resistors, capacitors, inductors, transistors,integrated circuits such as sensors, and other components.

To damp vibrations over a wide vibration-frequency band, the combinationof the PCB 22 and the isolation structure 26 is configured to have arelatively low natural frequency (i.e., a relatively large timeconstant) so that the isolation-structure-PCB combination resistshigher-frequency vibrations while still dissipating energy imparted tothe PCB by the vibrations. That is, the combination of the PCB 22 andthe isolation structure 26 is configured to have a fundamental resonantmode at a frequency that is significantly lower than the anticipatedfrequencies of a shock-induced vibration. For example, theisolation-structure-PCB combination is configured to have a fundamentalresonant mode in a natural-frequency band that starts from below, andincludes, approximately 100 Hz, which corresponds to a time constant inan approximate range of 0.010 seconds and higher.

But to have a relatively low natural frequency and a relatively largetime constant, the isolation structure 26 has a relatively large x-y“sway space” 30, which is a space between the PCB mount 24 within whichthe isolation-structure-PCB combination can sway (and rotate) indifferent directions within the x-y plane to dissipate energy from theshock-induced vibration. The isolation structure 26 also can beconfigured to allow swaying of the isolation-structure-PCB combinationin the z dimension, which is the dimension normal to the surface of thePCB 22 (the z component of the sway space is not labeled in FIG. 2).Alternatively, the isolation structure 26 can be configured to allow thePCB 22 to sway only, or primarily, in the z dimension.

Unfortunately, designing the isolation structure 26 to provide arelatively large sway space increases the sizes and masses of at leastthe isolation structure and the mount 24; and designing theisolation-structure-PCB combination to have a relatively low naturalfrequency can increase the size and mass of the PCB 22 as well. And if asubsystem including the PCB assembly 20 is packaged, then designing theisolation structure 26 to provide a relatively large sway space, anddesigning the isolation-structure-PCB to have a relatively low naturalfrequency, also can increase the size and the mass of the package, and,therefore, also can increase the size and the mass of the packagedsubassembly.

Still referring to FIG. 2, a conventional way to reduce the sway space,or to eliminate the isolation structure 26 altogether, is to “stiffen”the PCB 22 (e.g., by making the PCB thicker), to add a filler (e.g., amold) between the PCB and a rigid part of the package (if the PCBassembly 20 is part of a packaged subassembly), or to both “stiffen” thePCB and to add a filler.

Unfortunately, increasing the stiffness of the PCB 22 or adding a filleralso can increase the size and mass of a subsystem that incorporates thePCB assembly 20.

Yet another problem with both of the above-described techniques is thatbecause every PCB or other platform is unique (e.g., different size,different shape, different component layout, different massdistribution, different natural frequency), a designer typicallydedicates a significant amount of design time, design effort, and designresources to “shock proof” the PCB or other platform. For example, adesigner typically custom designs the mount 24 and the isolationstructure 26 for each different PCB 22.

Fortunately, described below are one or more embodiments of an assemblythat solves one or more of the above-described problems, and that mayprovide additional advantages. For example, an embodiment of an assemblycan be configured to isolate a PCB from a transient shock passively,actively, or by a hybrid passive-active technique.

For example, an embodiment of an assembly that solves one or more of theabove-described problems is configured to cancel (partially or fully),in an active manner, vibrations experienced by a PCB or by anotherplatform, whether the vibrations are induced by a shock or by anotherphenomena. The concept of actively cancelling vibrations experienced bya PCB, or by another platform, is similar to the concept of activelycancelling background noise that one might otherwise hear while he/sheis listening to music with headphones in a noisy environment.

Further in example, an embodiment of such an assembly includes aplatform (e.g., a PCB), a sensor, and a vibration-isolation assembly,which includes vibration-cancelling circuit and either self-sensingpiezoelectric actuators or vibration sensors with vibration-cancellingactuators. The sensor is mounted to the platform and is configured togenerate a sense signal that represents a vibration induced (e.g., ashock-induced vibration) of the platform. And the vibration-cancellingcircuit is configured to reduce a level of the vibration in response tothe sense signal. For example, the vibration-cancelling system isconfigured to reduce a level of a vibration induced in platform, or toeliminate the vibration altogether, by generating, in the platform, acounter vibration that has a magnitude approximately equal to amagnitude of the induced vibration and that has a phase approximatelyopposite to the phase of the induced vibration. That is, the countervibration partially or fully cancels the induced vibration such that thenet vibration that the platform experiences is reduced to approximatelyzero. Alternatively, the vibration-cancelling system is configured toreduce a level of a vibration induced in a platform by effectivelystiffening at least a portion of the platform to dampen the vibration.

Yet further in example, an embodiment of a method includes generating asense signal that represents a first vibration of a platform, andreducing a level of the first vibration by generating, in response tothe sense signal, a second vibration in the platform. For example, asensor generates a sense signal representing a first vibration induced(e.g., a shock-induced vibration) in the platform. And avibration-cancel circuit reduces or eliminates a level of the firstvibration in response to the sense signal. For example, thevibration-cancel circuit reduces a magnitude of a first vibrationinduced in a platform, or eliminates the first vibration altogether, bygenerating, in the platform, a second vibration having a magnitudeapproximately equal to the magnitude of the first vibration and having aphase approximately opposite to the phase of the first vibration. Thatis, the second vibration cancels the first vibration to reduce the netvibration that the platform experiences.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of a shock response spectrum (SRS), which is afrequency spectrum of a shock-induced vibration experienced by a PCB ofa subassembly such as an Inertial Measurement Unit (IMU).

FIG. 2 is an isometric plan view of a PCB assembly that includes a PCB,a mount, and a vibration-isolation structure disposed between the PCBand the mount.

FIG. 3 is an isometric plan view of a PCB assembly equipped with activevibration cancelling, according to an embodiment.

FIG. 4 is a cutaway side view of a portion of the PCB of FIG. 3,according to an embodiment.

FIG. 5 is a diagram of vibration-sense-and-cancel circuit of the PCBassembly of FIGS. 3-4, according to an embodiment.

FIG. 6 is a cutaway side view of a portion of the PCB of FIG. 3,according to another embodiment.

FIG. 7 is a diagram of a system that includes at least one of the PCBassembly of FIGS. 3-4, according to an embodiment.

DETAILED DESCRIPTION

Each value, quantity, or attribute herein preceded by “substantially,”“approximately,” “about,” a form or derivative thereof, or a similarterm, encompasses a range that includes the value, quantity, orattribute ±20% of the value, quantity, or attribute, or a range thatincludes ±20% of a maximum difference from the value, quantity, orattribute, or ±20% of the difference between the range endpoints. Forexample, an “approximate” range of b−c is a range of b−20%·(c−b) toc+20%·(c−b). Furthermore, the terms “a,” “an,” and “the” can indicateone or more than one of the objects that they modify.

FIG. 3 is an isometric plan view of a PCB assembly 40, which is equippedwith active vibration sensing and cancelling, according to anembodiment. Actively sensing and actively cancelling vibrations, such asshock-induced vibrations, in a PCB or other platform, can reduce oreliminate negative phenomena caused by such vibrations. For example,active vibration sensing and cancelling can reduce or eliminatevibration-induced damage to a PCB and to components mounted to the PCB,and can reduce or eliminate vibration-induced error in signals output bycomponents mounted to the PCB, such components including, for example,MEMS accelerometers and MEMS tuning fork gyroscopes (TFG). Furthermore,active vibration sensing and cancelling can allow a designer to omit avibration-isolation structure (such as the structure 26 of FIG. 2) fromthe PCB assembly 40, and can allow the designer the option of notstiffening a PCB board of the PCB assembly; consequently, activevibration sensing and cancelling can allow a reduction in the size andthe mass of a PCB assembly. And even for a PCB assembly including avibration-isolation structure, active vibration sensing and cancellingcan allow a reduction in the size of such a structure by, for example,allowing a reduction in the size of the sway space, and can allow areduction in the mass of such a structure by, for example, allowing aPCB not to be stiffened.

The PCB assembly 40 includes a PCB 42, a PCB mount 44, and an optionalvibration-isolation structure 46. The PCB 42 can be similar to the PCB22 of FIG. 3, except that the PCB 42 can have a reduced level ofstiffness, and thus a reduced mass, as compared to the PCB 22. The PCBmount 44 can be similar to the PCB mount 24 of FIG. 2. And thevibration-isolation structure 46 can be similar to thevibration-isolation structure 26 of FIG. 3, except that the structure 46can have a reduced sway space, a reduced overall size, and a reducedmass as compared to the structure 26. Furthermore, although not shown inFIG. 3, the PCB assembly 40 can be disposed, partially or fully, withina package (e.g., an epoxy package) alone or with one or more othercomponents or assemblies.

The PCB assembly 40 also includes active vibration control in the formof a vibration-sense-and-cancel circuit (for example, described below inconjunction with FIGS. 5 and 7) configured to sense and cancel,partially or fully, vibrations induced in the PCB 42 by, for example, atransient shock caused by the environment or another external phenomena.The circuit includes one or more sensors 48 (one sensor shown in FIG. 3)configured to sense vibrations in the PCB 42, and one or more actuators50 (three shown in FIG. 3) configured to generate vibrations thattogether counteract, in an active manner, the sensed vibrations. Thecircuitry also may include self-sensing piezoelectric actuators eachshunted by an external shunt damping circuit that is configured as anegative capacitance circuit (not shown in FIG. 3) configured to reducethe capacitance of the actuator in response to a shock vibration. Forexample, the sensors 48 can be accelerometers that are each configuredto sense a respective acceleration in one, two, or three dimensions, andthe one or more actuators 50 can each be a respective transducer, suchas a piezoelectric transducer or a heater, that is configured to alterits shape, or the shape of the PCB 42, in response to an appliedelectrical control signal. In addition, one or more of the actuators 50each can be a respective self-sensing piezoelectric actuator, which isconfigured to sense acceleration and to provide a response as anactuator driven by a negative capacitance circuit. Furthermore, one ormore of the sensors 48 or portions thereof, or one or more of theactuators 50 or portions thereof, or one or more of the self-sensingpiezoelectric actuators, can be disposed in locations other than on asame side of the PCB 42. For example, one or more of the sensors 48 orportions thereof, one or more of the actuators 50, or one or more of thesensing piezoelectric actuators or portions thereof, can be embeddedinside of the PCB 42, or can be disposed on different sides of the PCB.Moreover, the vibration-sense-and-cancel circuit can include components,such as sensing actuators that are each configured to function as both asensor 48 and an actuator 50.

The PCB assembly 40 also can include an energy harvester (which may ormay not form part of the vibration-sense-and-cancel circuit, and whichis not shown in FIG. 3) that operates as vibration damper to convert atleast a portion of an induced vibration that the PCB 42 experiences intoheat or any other kind of energy, such as into electrical energy for useby a system of which the PCB assembly 40 forms a part.

The vibration-cancellation effect also can be achieved by a method oftencalled “piezoelectric shunt damping (PSD),” in which each of one or moreself-sensing piezoelectric actuators is connected to an active externalshunt circuit that is configured to control the effective elasticstiffness of the actuator.

Still referring to FIG. 3, alternate embodiments of the PCB assembly 40are contemplated. For example, the shapes of the PCB 42, the PCB mount44, and the vibration-isolation structure 46 can be other than round.Furthermore, although described as having components mounted to a topside (the side visible in FIG. 3) of the PCB 42, the PCB assembly 40 caninclude one or more components mounted to a bottom side of the PCB.Moreover, one or more of the sensors 48 and the actuators 50 can bedisposed between the PCB 42 and the PCB mount 44 along the periphery ofthe PCB, for example, in, or forming part of, the vibration-isolationstructure 46, and can be configured, respectively, for sensing and forcancelling, either partially or fully, vibrations induced in the PCB inany of three (i.e. x-y-z) dimensions. In addition, embodiments describedabove in conjunction with FIGS. 1-2 and below in conjunction with FIGS.4-8 may be applicable to the PCB assembly 40 of FIG. 3.

FIG. 4 is a cutaway side view of the PCB assembly 40 of FIG. 3,according to an embodiment in which at least one of the actuators 50 isembedded, or is otherwise disposed, in the PCB 42. In FIG. 4, likereference numbers label like components common to FIGS. 3-4.

In addition to embedded actuators 50 (three embedded actuators 50 a-50 care shown in FIG. 4, the PCB assembly 40 includes at least onecontroller 60, which is mounted to the PCB 42 and which forms part ofthe vibration-sense-and-cancel circuit (not shown in FIG. 4). The PCBassembly 40 also can include one more actuators 50 that are disposed ona surface of the PCB 42 such as described above in conjunction with FIG.3.

In an embodiment in which the actuator 50 b is, for example, apiezoelectric transducer, conductive vias 62 a and 62 b electricallycouple the transducer 50 b to the controller 60, which is configured todrive the transducer, by way of the vias, with an electrical controlsignal (e.g., a control voltage) that causes the transducer to vibratein a manner that tends to cancel the vibration induced in the PCB 42.The other actuators 50 a, 50 c, and any other embedded actuator notshown in FIG. 4, can be electrically coupled to the controller 60 withrespective similar vias that are not shown in FIG. 4. Furthermore, anactuator 48 disposed on an upper surface 64 of the PCB 42 can be coupledto the controller 60 by one or more conductive traces (not shown in FIG.4) disposed on the upper surface, and an actuator disposed on a lowersurface 66 of the PCB can be coupled to the controller by one or morevias and one or more corresponding conductive traces (not shown in FIG.4) disposed on the lower surface.

And in an embodiment in which the actuator 50 b is, for example, apiezoelectric transducer that is configured as a sensing actuator tofunction as both an actuator and a sensor, conductive vias 62 a and 62 belectrically couple a drive signal from the controller 60 to thetransducer 50 b as described above, and conductive vias 64 a and 64 belectrically couple a sense signal from the transducer to thecontroller. The piezoelectric transducer 50 b is configured to generate,in response to a force (e.g., a vibration-induced force) that contortsthe shape of the transducer from its at-rest shape or steady-stateshape, a voltage having an amplitude that is proportional to the degreeof deformity that the transducer experiences relative to itssteady-state shape. The vias 64 a and 64 b are configured to couple thissense voltage from the transducer 50 b to the controller 60, which isconfigured to determine the magnitude and phase of the vibration beingexperienced by the PCB 42 at the transducer 50 b in response to thesense voltage. For each of the other actuators 50 a, 50 c, and for eachof any other embedded actuator not shown in FIG. 4, that are alsoconfigured to function as vibration sensors, a respective pair of viasthat are not shown in FIG. 4 can couple the respective sense signal tothe controller 60. Furthermore, an actuator also configured as a sensorand disposed on the upper surface 64 of the PCB 42 can be configured tocouple its sense signal to the controller 60 by way of one or moreconductive traces (not shown in FIG. 4) disposed on the upper surface,and an actuator also configured as a sensor and disposed on the lowersurface 66 of the PCB can be configured to couple its sense signal tothe controller by way of one or more vias and one or more correspondingconductive traces (not shown in FIG. 4) disposed on the lower surface 66of the PCB.

Still referring to FIG. 4, alternate embodiments of the PCB 40 arecontemplated. For example, instead of including a single controller 60,the PCB assembly 40 may include one or moreMultiple-Input-Multiple-Output (MIMO) controllers, one or multichannelcontrollers, or multiple controllers 60. Furthermore, the PCB assembly40 can include one or more signal-driver circuits (not shown in FIG. 4),each configured to drive a respective actuator with a control signalfrom a controller. Moreover, embodiments described above in conjunctionwith FIGS. 1-3 and below in conjunction with FIGS. 5-8 may be applicableto the PCB assembly 40 of FIG. 4.

FIG. 5 is a diagram of a vibration-sense-and-cancel circuit 70 of thePCB assembly 40 of FIGS. 3-4, according to an embodiment. In FIG. 5,like reference numbers label like components common to FIGS. 3-5.

In addition to a vibration sensor 48, an actuator 50, and a controller60, the circuit 70 includes an optional driver 72 and a feedback network74. Furthermore, the components of the circuit 70 other than the sensor48 can be called, collectively, a vibration-cancel circuit. For example,the actuator 50, controller 60, driver 72 (if present), and feedbacknetwork 74 together form a vibration-cancel circuit 76. Moreover, thevibration-sense-and-cancel circuit 70 forms a feedback loop 78.

As described above in conjunction with FIGS. 3-4, the vibration sensor48 is configured to sense a vibration of the PCB 42 in a dimension(e.g., the z dimension) at the location of the sensor, and to generatean electrical sense signal that represents the sensed vibration. Forexample, if the sensor 48 is an accelerometer, then the sensor can beconfigured to generate the amplitude of the sense signal at any giventime to be proportional to a sensed acceleration of the PCB 42 at thelocation of the sensor at the given time and in a given dimension (e.g.,the z dimension). Alternatively, if the sensor 48 is a piezoelectrictransducer, then the sensor can be configured to generate the amplitudeof the sense signal at any given time to be proportional to a senseddisplacement of the PCB 42, at the location of the sensor, from thelocation's steady-state position (e.g., z=0) at the given time and in agiven dimension (e.g., the z dimension).

In an example in which the actuator 50 is a self-sensing piezoelectrictransducer, the circuit 70 modulates the stiffness of the actuator 50 inresponse to the vibrations sensed by the actuator 50 itself (in thisexample, because the actuator 50 is self-sensing, the sensor 48 can beomitted). Hence, a vibration-cancellation effect is achieved byparametric modulation of the actuator 50 either attached to, orencapsulated in, the PCB 42 (FIG. 4). Such a noise-cancellation methodis called piezoelectric shunt damping (PSD), in which a self-sensingpiezoelectric actuator 50 is connected to an active external shuntcircuit that controls the effective elastic stiffness of the actuator.That is, the stiffness of the actuator 50 is modulated so that theactuator effectively stiffens a local section of the PCB 42 and,therefore, changes the PCB transfer function and, as a result, reducesthe vibration amplitude.

In an alternative embodiment, the actuator 50 is configured to vibrate,instead of to act as a damper, in response to a control signal from thedriver 72 (or directly from the controller 60 if the driver is notpresent). For example, if the actuator 50 is a piezoelectric transducer,then the control signal causes a region of the transducer to bedisplaced by a distance (from a steady-state position of the transducer)that is proportional to the amplitude of the control signal in adimension (e.g., the z dimension); and because the transducer is coupledto the PCB 42, the transducer displaces a corresponding location of thePCB by a distance (from a steady-state position of PCB region) that isproportional to the amplitude of the control signal and that is in thesame dimension.

The controller 60 is configured to sense a feedback signal from thefeedback network 74, and to drive the actuator 50 (via the driver 72 ifpresent) in a manner that tends to reduce, toward or to zero, amagnitude of the feedback signal. Said another way, in an example inwhich the actuator 50 is configured to generate a cancellation vibrationinstead of being configured to act as a damper, the noise-cancellationapproach is based on the principle of superposition, in which generateda cancelling signal has the same amplitude but opposite phase as thevibration. As a result, superimposing the cancelling vibration and theinduced vibration ideally yields a net vibration of zero because thesetwo vibrations ideally cancel each other such that the vibration sensor48 senses zero vibration, because the induced vibration is cancelled bythe actuated vibration. In another example, as shown in dashed line inFIG. 5, a cancellation signal that represents the cancelling vibrationof the actuator 50 can be input to the controller 60, which isconfigured to add the feedback signal and the cancellation signal, andto drive the actuator so as to drive the sum of these signals to ortoward zero. The sum of the cancellation and feedback signalsapproximately equaling zero indicates that the actuated vibration isapproximately cancelling the induced vibration. Furthermore, thecontroller 60 can be any suitable type of control circuit, such as ananalog or digital proportional-integral-derivative (PID) controller thatincludes one or more analog or digital error amplifiers.

Still referring to FIG. 5, the optional driver 72 can be any suitablepower-amplifier circuit that is configured to boost the power of thecontrol signal to a level that is suitable for driving the actuator 50.

And the feedback network 74 can be any suitable active or passive analogor digital circuit configured to condition the sense signal from thesensor 48 for input to the controller 60. For example, the feedbacknetwork 74 can be configured to alter the amplitude of the sense signalto be in a range specified for input to the controller 60. Furthermore,the feedback network 74 can be configured to filter the sense signal, orto add an offset voltage or current to the sense signal. For example,the feedback network 74 can be characterized by a transfer function thataffects the stability of the closed-loop circuit 70, and low-pass andhigh-pass filters can be a part of the feedback network or otherwise canbe part of the closed-loop network transfer function. For example, thefeedback network 74 can be configured to include, or otherwise tofunction as, a low-pass filter that is configured to filter outhigher-frequency components of the sense signal. Still referring to FIG.5, alternate embodiments of the vibration-sense-and-cancel circuit 70are contemplated. For example, although shown as including one sensor 48and one actuator 50, the circuit 70 may include more than one sensor ormore than one actuator. Furthermore, although described as including onefeedback loop 78, the circuit 70 can include multiple feedback loopsthat are controlled by the same, or by respective, controllers 60.Moreover, although described as being configured to sense vibration andto vibrate, respectively, in a single same dimension, the sensor 48 maybe configured to sense vibration in multiple dimensions, and theactuator 50 may be configured to displace the PCB 42 in multipledimensions that may be the same as, or different than, the dimensions inwhich the sensor is configured to sense vibration. In addition, the PCBassembly 40 may include multiple circuits 70, one circuit per vibrationsensor 48 or per actuator 50, or one circuit per dimension of the sensor48 or actuator 50. Furthermore, the circuit 70 may include a feedforwardcomponent, or a prediction component, for better tracking of the cancelvibration generated by the actuator 50 to the actual vibration sensed bythe sensor 48. Moreover, the circuit 70 can include a digital signalprocessor (DSP) to achieve vibration cancellation by digital activenoise cancellation, which utilizes adaptive filtering of a referencesignal supplied to the actuator 50. Hence, the error between theexternally induced vibration and the vibration generated by the actuator50 is driven toward or to zero by a reference signal tuned by anadaptive filter. An adaptive filter has the ability to adjust itsimpulse response or transfer-function to match desired systemcharacteristics. For example, vibration cancellation can be achieved byexecuting a conventional Filtered-X least mean square (FXLMS) algorithm,which configures the adaptive filter to correlate the reference signalwith the input signal (the signal representing the sensed vibration ofthe PCB 42 (FIG. 4). Moreover, embodiments described above inconjunction with FIGS. 1-4 and below in conjunction with FIGS. 6-8 maybe applicable to the vibration-sense-and-cancel circuit 70 of FIG. 5.

Referring to FIGS. 3-5, operation of the vibration-sense-and-cancelcircuit 70 is described, according to an embodiment in which the sensor48 senses vibration in a single dimension (e.g., the z dimension), andthe actuator 50 is configured to vibrate the PCB 42 in the same singledimension.

PCB vibration can be described as superposition of the natural modesexited by a transient signal which includes different frequencies. ASin/Cos-like signal describes a single frequency transient signal.Cancellation signal can be generated at different locations of the PCB42 (FIG. 4) such that the superposition of the generated signal with theexternally induced vibration decreases the total vibration in one ormore desired locations of the PCB.

Consequently, a vibration-cancellation device (e.g., one or moreactuators 50) that can generate a distributed vibration over the PCB 42,i.e., that can generate at one or more points of the PCB, a respectivevibration defined by a cancel-vibration vector that is approximatelyequal in magnitude yet approximately opposite in phase to theinduced-vibration vector corresponding to the same point, can cancel,partially or fully, an induced vibration experienced by the PCB.

And because the vibration-cancel circuit 76 is configured to cancelvibration induced in the PCB 42 in an active manner using negativefeedback, a designer need not redesign, or modify, thevibration-sense-and-cancel circuit 70 for each different version or typeof PCB, except possibly to add more sensors 48 and actuators 50 tolarger PCBs, and possibly to reduce the number of sensors and actuatorsfrom smaller PCBs. Consequently, including thevibration-sense-and-cancel circuit 70 as part of the PCB assembly 40 canreduce the design time of the PCB assembly significantly.

Still referring to FIGS. 3-5, in operation, the sensor 48 senses avibration of the PCB 42 at the location of the sensor in the zdimension, and generates a sense signal that represents the profile(e.g., the magnitude, frequency, and phase) of the sensed vibration. Forexample, if the sensor 48 is an accelerometer, then the sensor generatesa sense signal having a magnitude that represents an acceleration of thelocation of the PCB 42 in the z dimension as a function of time.

The feedback network 74 converts the sense signal into a feedbacksignal. For example, the feedback network 74 can attenuate or amplify(if the feedback network is an active network) the sense signal, canfilter the sense signal (e.g., can function as a low-pass filter or abandpass filter), and can shift the phase or the offset of the sensesignal. The feedback network 74 may so modify the sense signal toprevent the loop 78 from oscillating, to render the amplitude of thefeedback signal compatible with the input-voltage or input-current rangeof the controller 60, or to filter out noise.

The controller 60 effectively compares the feedback signal to zero, orcompares the feedback signal to the cancellation signal if present, andgenerates the control signal to have at least one characteristic thattends to reduce the amplitude of the feedback signal toward or to zero,or to reduce the difference between the amplitudes of the feedback andcancellation signals to or toward zero. For example, because the loop 78is a negative feedback loop, the controller 60 generates the controlsignal having an amplitude that causes the actuator 50 to generate acancel vibration having a magnitude that is approximately equal to themagnitude of the induced vibration sensed by the sensor 48, and having aphase that is shifted by approximately 180° relative to the phase of thevibration sensed by the sensor.

The driver 72, if present, effectively increases the power of thecontrol signal to a level suitable to drive the actuator 50. Forexample, if the actuator 50 has a relatively high input capacitance,then the driver 72 may source an output current that is high enough todrive the actuator at a given frequency and at a given slew rate.

The circuit 70 operates in the above-described manner until themagnitude of the feedback signal at least approximately equals zero, oruntil the difference between the magnitudes of the feedback andcancellation signals approximately equals zero.

Still referring to FIGS. 3-5, alternate embodiments of the operation ofthe vibration-sense-and-cancel circuit 70 are contemplated. For example,there may be one circuit 70 for each pair of a sensor 48 and an actuator50, or a single controller 60 and feedback network 74 can be used formultiple sensor/actuator pairs. Furthermore, if the sensor 48 andactuator 50 are a same device, then the input of the feedback network 74is coupled to a sensor-signal output of the actuator/sensor. Moreover, asingle sensor 48 can be configured to measure vibration in multipledimensions, in which case there may be a separate circuit 70 for eachdimension, which means that there may be multiple circuits 70 for eachsensor. Similarly, a single actuator 50 can be configured to measurevibration in multiple dimensions, in which case there may be a separatecircuit 70 for each dimension, which means that there may be multiplecircuits 70 for each actuator. In addition, instead of receiving a sensesignal from a vibration sensor 48, the feedback network 74 may receivean error signal from a measurement component, such as a MEMS tuning forkgyroscope (TFG), such that the circuit operates to reduce an error in asignal generated by the measurement component. Furthermore, instead ofoperating in a closed-loop mode, the circuit 70 can be configured tooperate in an open-loop mode. For example, the circuit 70 may include anamplifier that receives the sense signal from the sensor 48, thatinverts and optionally amplifies the sense signal, and that drives theactuator 50 with the inverted and optionally amplified signal such thatthe actuator generates a vibration that is, at least ideally, equal inmagnitude and opposite in phase to the vibration that the sensor sensed.

FIG. 6 is a cutaway side view of a portion of the PCB assembly 40 ofFIG. 3, according to an embodiment in which at least one of theactuators 50 is embedded, or is otherwise disposed, in the PCB 42, andin which the actuators are heat elements such as resistors that generateheat in response to conducting an electric current.

Each of the heat elements 50 a-50 c can be coupled to the controller 60(FIG. 5) with respective vias (not shown in FIG. 6) in a manner similarto that described above in conjunction with FIG. 4.

In an embodiment, the controller 60 (FIG. 5) is configured to drive eachof the heat elements 50, by way of the vias (not shown in FIG. 6), witha respective electrical control signal (e.g., a control current) thatcauses the heat element to vibrate the PCB 42 in a manner that tends tocancel a vibration induced in the PCB (e.g., a shock-induced vibration).In response to being activated, a heat element 50 heats a location ofthe PCB 42 at which the heat element is located, and the heat contortsthe shape of the PCB at the location. For example, the heat may causethe PCB 42 to bend or bow at the location. And in response to the heatelement 50 being deactivated, the location of the PCB 42 cools andreturns to its steady-state shape. If the heat-conduction time constantof the heating element 50 and the location of the PCB 42 is smallenough, then the controller 60 can control the heating element so thatthe location of the PCB 42 vibrates in a manner that partially or fullycancels a vibration induced at the location (and possibly at otherlocations) of the PCB as described above in conjunction with FIGS. 3-5.

In another embodiment, the controller 60 (FIG. 5) is configured to driveeach of the heat elements 50, by way of the vias (not shown in FIG. 6),with a respective electrical control signal (e.g., a control current)that activates the heat element to cause the PCB 42 to withstand avibration induced in the PCB. For example, suppose a shock-induced forceis applied in the −z direction to a location of the PCB 42 at which theheat element 50 is located (or to a location near the heat element). Thecontrol 60 is configured to apply, to the heat element 50, a controlsignal that causes the heat element to generate heat, which, in turn,causes the location of the PCB 42 to bend in the −z dimension such thatthe peak of the bend is the highest point of the location along the zaxis. The bend distributes the shock-induced force over a larger area ofthe PCB 42 much like an arch over a door or window distributes forcefrom the center of the door/window to the sides of the door/window.Viewed another way, the bend effectively stiffens the PCB 42 to dampendown the induced vibration. The result of the heat-induced bend is thatthe PCB 42 is better able to withstand the shock-induced force, and,therefore, to better withstand any accompanying shock-induced vibration.In response to a sensor 48 (FIG. 5) sensing that the force or vibrationhas dissipated, the controller 60 deactivates the heat element 50; inresponse to the deactivation of the heat element, the location of thePCB 42 cools and returns to its steady-state shape.

Still referring to FIG. 6, alternate embodiments of the PCB assembly 40and the heat elements 50 are contemplated. For example, one or more heatelements 50 can have orientations (e.g., extending lengthwise in the zdimension) other than the orientations shown in FIG. 6. Furthermore, thePCB 42 can include one or more heat elements 50, and one or more othertypes of actuators 50 (e.g., piezoelectric transducers, sensor/actuatorcombinations). Moreover, embodiments described above in conjunction withFIGS. 1-5 and below in conjunction with FIGS. 7-8 may be applicable tothe PCB assembly 40 and heating elements 50 of FIG. 6.

Referring to FIGS. 3-6, in another embodiment, each of one or more ofthe actuators 50 can be replaced with a respective energy-harvestingcomponent. The control circuit 60 can generate the control signal toadjust the stiffness of the energy-harvesting component as describedabove to reduce vibration of the PCB 42. And the energy-harvestingcomponent can dampen the vibration by converting at least a portion ofthe vibration energy into another form of energy such as electricalenergy that can be used by one or more circuits on the PCB 42. And thePCB 42 can include one or more circuits to convert electrical energyharvested by the energy-harvesting component into one or more voltagessuitable to power the one or more circuits.

FIG. 7 is a diagram of a system 90, which incorporates one or more PCBassemblies 40 (FIG. 3), or one or more other platform assemblies withactive vibration cancellation, according to an embodiment. For purposesof example, the system 90 is described as including one PCB assembly 40,it being understood that the description is similar if the systemincludes more than one PCB assembly 40, or includes one or more otherplatform assemblies equipped with active vibration cancellation.

The system 90 includes a movable apparatus 92, a subsystem 94 disposedon the movable apparatus, and a PCB assembly 40 disposed on thesubsystem.

The movable apparatus 92 can be a vehicle such as an aircraft,watercraft, land craft, spacecraft, drone, or any other movable objector any other object subject to vibration. For example, the apparatus 92can be apparatus, such as a washing machine, that vibrates during normaloperation, even in the absence of a shock vibration or other externallyinduced vibration.

The subsystem 94 can be any suitable subsystem such as a navigation orflight-management subsystem that includes an inertial measurement unit(IMU), a communication subsystem, a steering subsystem, or a propulsionsubsystem.

And the PCB assembly 40 can be, can include, or can form a part of anysuitable component such as a measurement component that is configured tomeasure a physical quantity such as linear or angular acceleration(e.g., a CVG), and that is configured to generate a sense signal thatrepresents the measured physical quantity.

Still referring to FIG. 7, alternate embodiments of the system 90 arecontemplated. For example, one or more embodiments described above inconjunction with FIGS. 1-7 may be applicable to the system 90.

From the foregoing it will be appreciated that, although specificembodiments have been described herein for purposes of illustration,various modifications may be made without deviating from the spirit andscope of the disclosure. Furthermore, where an alternative is disclosedfor a particular embodiment, this alternative may also apply to otherembodiments even if not specifically stated. Moreover, the circuitcomponents described above may be disposed on a single or multipleintegrated-circuit (IC), a digital signal processor (DSP), a filter anddetect (FAD) circuit, integrated-photonic (IP) dies, orradio-frequency-over-glass (RFOG) dies to form one or moreICs/IPs/RFOGs/DSP/FAD, where these one or more ICs/IPs/RFOGs/DSP/FAD maybe coupled to one or more other ICs/IPs/RFOGs/DSP/FAD. Furthermore, oneor more components of a described apparatus or system may have beenomitted from the description for clarity or another reason. Moreover,one or more components of a described apparatus or system that have beenincluded in the description may be omitted from the apparatus or system.

Example Embodiments

Example 1 includes a method, comprising: sensing a vibration of aplatform; and displacing the platform in response to the sensedvibration and in a manner that counteracts, at least partially, adisplacement of the platform caused by the vibration.

Example 2 includes the method of Example 1 wherein displacing theplatform includes inducing, in the platform, a counteracting vibrationthat is out of phase with the vibration of the platform.

Example 3 includes the method of any of Examples 1-2 wherein displacingthe platform includes inducing, in the platform, a bend that dampens thevibration.

Example 4 includes a method, comprising: generating a sense signal thatrepresents a first vibration of a platform; and reducing a level of thefirst vibration by generating, in response to the sense signal, a secondvibration in the platform.

Example 5 includes the method of Example 4 wherein generating the sensesignal includes generating the sense signal with a sensor.

Example 6 includes the method of any of Examples 4-5 wherein generatingthe sense signal includes generating the sense signal with anaccelerometer.

Example 7 includes the method of any of Examples 4-6 wherein generatingthe sense signal includes generating the sense signal with an actuator.

Example 8 includes the method of any of Examples 4-7 wherein generatingthe sense signal includes generating the sense signal with aself-sensing piezoelectric actuator.

Example 9 includes the method of any of Examples 4-8 wherein generatingthe sense signal includes generating the sense signal with a sensordisposed over a surface of the platform.

Example 10 includes the method of any of Examples 4-9 wherein generatingthe sense signal includes generating the sense signal with a sensordisposed at least partially within the platform.

Example 11 includes the method of any of Examples 4-10, furthercomprising: generating a control signal in response to a feedback signalthat is related to the sense signal; and wherein reducing includesreducing the level of the first vibration by generating the secondvibration in response to the control signal.

Example 12 includes the method of any of Examples 4-11, furthercomprising: generating a control signal in response to a feedback signalthat is related to the sense signal; and wherein reducing includesreducing the level of the first vibration, as represented by the sensesignal, by generating the second vibration in response to the controlsignal.

Example 13 includes the method of any of Examples 4-12, furthercomprising: generating a control signal in response to a feedback signalthat is related to the sense signal; and wherein reducing includesreducing the level of the first vibration, as represented by thefeedback signal, by generating the second vibration in response to thecontrol signal.

Example 14 includes the method of any of Examples 4-13, furthercomprising: generating a control signal; varying the control signal inresponse to a feedback signal that is related to the sense signal so asto cause the feedback signal to dither around a minimum value; andwherein reducing includes cancelling, at least partially, the firstvibration by generating the second vibration in response to the controlsignal.

Example 15 includes the method of any of Examples 4-14, furthercomprising determine an angular velocity about a sense axis of agyroscope attached to the platform.

Example 16 includes a method, comprising: generating a sense signal thatrepresents a vibration of a platform; changing, in response to the sensesignal, a characteristic of the platform to counteract, at leastpartially, the vibration of the platform.

Example 17 includes the method of Example 16 wherein changing thecharacteristic includes changing a shape of the platform.

Example 18 includes the method of any of Examples 16-17 wherein changingthe characteristic includes changing a shape of the platform by heatingthe platform.

Example 19 includes the method of any of Examples 16-18 wherein changingthe characteristic includes changing an effective elastic stiffness ofthe platform.

Example 20 includes the method of any of Examples 16-19 wherein changingthe characteristic includes changing an effective elastic stiffness of aself-sensing piezoelectric actuator mechanically engaged with theplatform.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiments shown. Therefore, it ismanifestly intended that this invention be limited only by the claimsand the equivalents thereof.

What is claimed is:
 1. A method, comprising: generating a sense signalthat represents a vibration of a platform; changing, by a plurality ofactuators coupled to a platform having a first surface and secondsurface opposite the first surface, a characteristic of the platform tocounteract, at least partially, the vibration of the platform, wherein afirst actuator of the plurality of actuators is either coupled to thefirst surface of the platform or at least partially embedded within theplatform, wherein a second actuator of the plurality of actuators iseither coupled to the second surface of the platform or at leastpartially embedded within the platform.
 2. The method of claim 1,wherein changing the characteristic includes changing a shape of theplatform.
 3. The method of claim 1, wherein changing the characteristicincludes changing a shape of the platform by heating the platform. 4.The method of claim 1, wherein changing the characteristic includeschanging an effective elastic stiffness of the platform.
 5. The methodof claim 1, wherein changing the characteristic includes changing aneffective elastic stiffness of a self-sensing piezoelectric actuatormechanically engaged with the platform.
 6. The method of claim 1,wherein generating the sense signal includes generating the sense signalwith a sensor.
 7. The method of claim 1, wherein generating the sensesignal includes generating the sense signal with an accelerometer. 8.The method of claim 1, wherein generating the sense signal includesgenerating the sense signal with an actuator.
 9. The method of claim 1,wherein generating the sense signal includes generating the sense signalwith a self-sensing piezoelectric actuator.
 10. The method of claim 1,wherein generating the sense signal includes generating the sense signalwith a sensor disposed over a surface of the platform.
 11. The method ofclaim 1, wherein generating the sense signal includes generating thesense signal with a sensor disposed at least partially within theplatform.
 12. The method of claim 1, wherein changing a characteristicof the platform to counteract, at least partially, the vibration of theplatform includes displacing a portion of the platform.
 13. The methodof claim 12, wherein displacing a portion of the platform includesdisplacing a portion of the platform in multiple dimensions.
 14. Themethod of claim 1, further comprising determining an angular velocityabout a sense axis of a gyroscope attached to the platform.
 15. Amethod, comprising: generating a sense signal that represents avibration of a platform; changing, in response to the sense signal, acharacteristic of the platform to counteract, at least partially, thevibration of the platform, wherein changing the characteristic includeschanging a shape of the platform.
 16. A method, comprising: generating asense signal that represents a vibration of a platform; changing, inresponse to the sense signal, a characteristic of the platform tocounteract, at least partially, the vibration of the platform, whereinchanging the characteristic includes changing a shape of the platform byheating the platform.